1. Field of the Invention
This invention relates to a production line for nonwoven fabrics obtained by needling.
A production line for non-woven fabrics by needling generally comprises the following machines:
a carding machine PA0 a blamire feed or spreader/batt-making machine PA0 a pre-needling device PA0 one or more needling devices PA0 a winding device PA0 subsequent manufacturing stages such as sizing, latexing etc.
2. Description of the Prior Art
The purpose of the carding machine is to produce a light, coherent, but delicate web from the individual fibres.
The purpose of the blamire feed is to lay this web in several superposed and progressively staggered layers, in order to achieve a lap or batt with a higher surface weight.
The purpose of the needling devices is to consolidate this lap through the interpenetration of the fibres and layers. Boards provided with very large numbers of vertical needles regularly strike down on the fibre lap passing horizontally below these needle boards. Fibres of the upper layers are carried by the needles towards the lower layers, and the result is a felting effect which gives the lap greater resistance, this resistance depending greatly on the density of penetration of the needles into the batt.
The winder receives the needled product and takes it, in the form of rolls adapted to the conveyance, to the subsequent manufacturing stages.
During needling of the batt supplied by the blamire feed, this batt undergoes changes as regards the distribution of the fibres.
The voluminal density of the material thus increases as the needling proceeds, so that the thickness of the batt is greatly reduced by the interpenetration of the fibres of the different layers.
Another type of distortion is often found in practice, namely a final uneven distribution over the width of the batt. It is thus found that the surface weight of the non-woven fabric on leaving the last needling device is lower at the centre of the batt than at the edges and that in fact, if samples of batt are taken across the whole width of the product, the curve giving the weight of the samples as a function of the position across the width of the batt is a more or less regular V-shape. The real shape of this curve, which will be called the V-curve below, depends, of course, on numerous factors, such as the type of fibres, weight of the batt, needling density etc.
The well-known disadvantage of this distortion of the batt is that the batt is sold by surface weight, and that the purchaser often considers as the price basis the minimum weight obtained from pre-washed samples across the width of the non-woven fabric. This is according to the criterion that a surplus of material often corresponds to an improvement in the product, and that the latter therefore can only be resold according to the least heavy zones of the product; without this attitude, the least heavy zones could be considered weak points and thus faults in the product, which would not then be top quality.
In considering the weight of the least heavy zones as the normal weight of the product, all the material present in the other zones, the weight of which exceeds that of the least heavy zones, constitutes lost material for the producer, since he cannot charge its value in the price which he charges the purchaser.
The V-shape obtained at the end of the production line thus constitutes a cause of loss of profitability in the process, which producers are obviously trying to minimize, but without being able to manage this perfectly.